1. Field of the Invention
The present invention relates to organic synthesis and, more particularly, to processes for preparing phenol or derivatives.
2. Description of the Prior Art
Oxygen-containing benzene derivatives such as phenol, dihydric phenols, benzoquinone, chlorophenols, cresols, ethylphenols, nitrophenols and the like are valuable products and find an extensive use for various applications. The most mass-scale prepared product of this class is phenol, the basic amount of which is intended for the production of phenolic resins, synthesis of adipic acid, caprolactam, bisphenol, nitro- and chlorophenols, phenol sulphonic acids and the like. Dihydric phenols are employed in photography, as well as antioxidants and modifying agents for stabilization plastics. Cresols are used for the production of cresol-formaldehyde resins; chlorophenols for the manufacture of herbicides; benzoquinone as a raw material for the preparation of hydroquinone and the like.
Known in the art is a principal possibility for preparing oxygen-containing benzene derivatives by way of a direct oxidation of benzene and derivatives thereof. However, all the attempts to carry out these reactions with an acceptable selectivity repeatedly undertaken during recent decades has proved to be unsuccessful. For example, the main products of oxidation of benzene with molecular oxygen, depending on conditions, are either maleic anhydride (on specially selected catalysts) or products of a complete oxidation, whereas phenol and benzoquinone are formed but in trace amounts. In a direct oxidation of benzene derivatives, such as toluene, the oxidation process affects the functional group in the first place with the formation of benzaldehyde and benzoic acid, but the formation of cresols is not observed (G. I. Golodetz. Heterogeneous-Catalytic Oxidation of Organic Compounds. Kiev, "Naukova Dumka" Publishing House, 1978, pp. 209-224).
There are a number of processes for the production of oxygen-containing benzene derivatives (L. Tedder, A. Nechvatal, A. Jubb. Industrial Organic Chemistry, Moscow, "MIR" Publishers 1977, pp. 198-205). In the preparation of phenol, the most widely used is the so-called cumene process accounting for more than 90% of the world output of phenol (J. Econ. and Eng. Review, 1982, vol. 14, No. 5, p. 47). This process consists of three stages:
alkylation of benzene with propylene to give cumene (isopropylbenzene);
oxidation of cumene to cumene hydroperoxide;
decomposition of cumene hydroperoxide with the formation of phenol and equimolar amounts of acetone.
This is a multi-stage process, and its efficiency depends to a great extent on the possibility for commercialization of acetone. However, recently there has been a declining trend in the demand for acetone which in the foreseeable future may result in the necessity of abandoning the cumene process (Kohn P. M., Bolton L., Cottrell R., McQueen S., Ushio S., Chem. Eng. (USA), 1979, vol. 86, No. 8, pp. 62-64).
Known in the art is a process for preparing phenol (Iwamoto M. Hirata J., Matsukami K., Kagawa S., J. Phys. Chem., 1983, vol. 87, No. 6, pp. 903-905) by way of oxidation of benzene with nitrous oxide at a temperature of 550.degree. C.-600.degree. C.: EQU C.sub.6 H.sub.6 +N.sub.2 O=C.sub.6 H.sub.5 OH+N.sub.2
In this case as the catalyst use is made of vanadium oxide, molybdenum oxide and tungsten oxide. To improve selectivity water vapors are added to the reaction mixture. The best results were obtained on a catalyst 3.3% V.sub.2 O.sub.5 /SiO.sub.2 at the temperature of 550.degree. C. at the following composition of the reaction mixture: 8.2% benzene, 16.9% nitrogen oxide and 30.7% water. Conversion of benzene under these conditions, X, was 10.7%, selectivity, S, gas 71.5% which corresponded to a yield, Y, of phenol of 7.7% (Y=X.S).
However, this process features an insufficient yield of phenol; the process requires a high temperature and introduction of water into the reaction mixture which necessitates additional power consumption for its evaporation and complicates isolation of the desired product. This process was not practiced on a commercial scale. This was apparently associated with an insufficient selectivity as well. The selectivity parameter is of a great importance for this reaction, since lowering of selectivity due to over oxidation means not only an increased benzene consumption, but especially high consumption of nitrous oxide.
To prepare more complex oxygen-containing benzene derivatives, two possibilities can be used. The first envisages introduction of a required functional group into the respective oxygen-containing benzene derivative; the second resides in a direct oxidation of the respective benzene derivative. The difficulties of carrying out the less complicated reaction of preparation of phenol from benzene would be also encountered in the production of other oxygen-containing benzene derivatives. But in this case, the problem of selectiveness is still more acute and, hence, that of the process efficiency, since the number of possible directions of the reaction (o-, p- and m-isomers, participation of functional groups in the chemical transformation) considerably increases.
For example, the process for preparing dihydric phenols is known which is effected in a manner similar to that of the cumene process for the preparation of phenol and which features a multi-stage character and the necessity of commercialization of acetone formed in large quantities (Vorozhtsov N. N. Foundations fo Synthesis of Intermediate Products and Dyestuffs. M., Goskhimizdat Publishers, 1955, p. 621). In this process, alkylation of benzene with propylene is effected in the first stage with propylene; in so doing, there is possible the formation of three isomers of diisopropyl and triisopropylbenzene. Then, the corresponding derivatives of diisopropylbenzene are oxidized into cumene hydroperoxides and, finally, decomposition of cumene dihydroperoxide is effected in the last stage of the process.
There is a number of processes for the preparation of dihydric phenols, as well as chlorophenols and phenolsulphonic acids based on an alkali treatment of corresponding chloro- and sulpho-benzene derivatives. These processes, however, necessitate the use of aggressive reagents--concentrated acids and alkalis and are accompanied by the formation of several tons of alkaline and acidic effluents per ton of the product, thus complicating the problem of the environment pollution.
Known in the art is another process for the preparation of oxygen-containing benzene derivatives, in particular phenol and chlorophenol (Suzuki E., Nakashiro K., Onoy Y., Chemistry Letters, 1988, No. 6, pp. 953-956). In this process, benzene or chlorobenzene in the vapor phase are subjected to oxidation with nitrous oxide on a pentasil-type catalyst of an alumosilicate composition with the ratio of SiO.sub.2 /Al.sub.2 O.sub.3 =85 at the temperature of 330.degree. C. with the following composition of the reaction mixture: 6.9 mol. % benzene, 51 mol. % nitrous oxide, nitrogen being the balance. The time of contact of the gas mixture with the catalyst is 2 seconds. The yield of phenol in this case is 5.5%. Under similar conditions (temperature 330.degree. C., 3.9% chlorobenzene, 71% nitrous oxide, the contact time--2 seconds) in the oxidation of chlorobenzene, yields of chlorophenol did not exceed 6.7%. The use of an alumosilicate catalyst as compared to the above-mentioned vanadium catalyst (Iwamoto M., Hirata J., Matsukami K., Kagawa S., J. Phys. Chem. 1983, vol. 87, No. 6, pp. 903-905) made it possible to substantially simplify the process by carrying out the same without introduction of water vapors into the reaction mixture. However, yields of phenol and chlorophenol in this process remained low, 5.5% and 6.7% respectively.
Known in the art is another process for phenol preparation (Gubelmann, et al. EP 341,165 and U.S. Pat. No. 5,001,280) by way of benzene oxidation with nitrous oxide. Like Suzuki, et al., Gubelmann, et al. make use of zeolite catalysts of aluminosilicate composition but of a greater SiO.sub.2 /Al.sub.2 O.sub.3 ratio ranging from 90 to 500. Higher phenol yields up to 16% at 400.degree. C. are shown but, nevertheless, such yields are not sufficiently high.
It is an object of the present invention to provide such a process for preparing oxygen-containing benzene derivatives which would make it possible to obtain the desired products in a sufficiently high yield following a simple procedure.